The present invention relates to a method for preparing glyoxylic acids and their derivatives. More particularly, the present invention relates to a method of preparing these compounds from acyl nitrile compounds.
Glyoxylic acids and their derivatives serve many specialized applications in the chemical arts. Amongst the most important of these is their use as photoinitiators and as intermediates for preparing photoinitiators.
U.S. Pat. No. 4,038,164 discloses the use of certain glyoxylic acid derivatives as photoinitiators. The particular compounds referred to by the patent are arylglyoxylate, ring-substituted arylglyoxylate and heterocyclic glyoxylate compounds. It is suggested that these compounds be prepared by the methods of U.S. Pat. Nos. 3,5312,737 and 3,065,259.
The several preparation routes disclosed in the first of these patents, U.S. Pat. No. 3,532,737; all utilize glyoxylic acid as a starting material. This compound is difficult to prepare and is not readily available.
The second patent, U.S. Pat. No. 3,065,259, requires the use of an organo-metallic compound and lithium halide; the reaction involved is highly exothermic and yields are relatively low.
It is also suggested that one of the preferred compounds of U.S. Pat. No. 4,038,164; namely the methyl ester of phenylglyoxylic acid, be prepared by the reaction of methyl oxalyl chloride with benzene in the presence of aluminum trichloride. While this method produces results which are generally acceptable, the relatively high cost of the required alkyl oxalyl chloride and the relatively low yield of the process are objectionable factors.
Another process which has been suggested is the oxidation of mandelic acid to form phenyl glyoxylic acid which is then esterified with methyl alcohol. This process is objectionable because the yields are low and the process produces excessive quantities of by-products which cannot be recycled.
U.S. Pat. No. 4,069,252 discloses yet another route for making these compounds. Example 4 of the patent teaches that phenylglyoxylic acid ethyl ester can be prepared by refluxing a solution of benzoyl cyanide in ethanol, in the presence of HCl, for 5 hours and then distilling-off excess ethanol. This method, however, is less than satisfactory because it leads predominantly to ethyl benzoate.
It is apparent from the foregoing that a need exists for a method for preparing glyoxylic acids and derivatives thereof which utilizes readily available raw materials and produces the desired products in high yields. We have found a new method for the preparation of glyoxylic acids and their derivatives which eliminates most of the aforementioned objections.